lipinski



March 24, 1964 H. s. LlPlNSKl 3,125,957

SLIDING FIN PROJECTILE Filed Feb. 25, 1962 INVENTOR.

HENRY S. LIPINSKI BY ATTORNEYS- United States Patent O 3,125,957 SLXDKNG FHN PROEECTILE Henry S. Lipinslri, Philadelphia, Pa, assignor to the United States of America as represented by the Secretar-y of the Army Filed Feb. 23, 1962, Ser. No. 175,373 5 Claims. (Cl. fill-50) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to an elongated projectile which is longer than 5 calibers for which stabilizing fins are provided because without such fins it is known that such a projectile is too long to be stabilized entirely by spin. With such elongated projectile fins have been found to need a sabot in order that the muzzle velocity of the projectile may be as high as desired, the sabot falling away after ejection from the gun. One proposal has contemplated -a sabot in front of the fins, but tests have shown inaccuracies in flight due to a number of causes. For one cause the side and bottom surfaces of the fins have been found subject to erosion of the hot gases moving past these fins. Another cause has been the aero-dynamic effect of heating the fins by the hot gases. An object of this invention is to provide a elongated projectile of the fin stabilized sort in which balloting and other errors in flight have been reduced to provide a projectile having a smaller probable error than has heretofore existed for the finned projectiles of a given length, size, and velocity.

The single figure of the drawing exemplifies a preferred embodiment for a projectile of the sort referred to with a propellant case before being fired.

An elongated projectile has a penetrator type body portion of to 20 calibers in length shown as being embodied in fixed ammunition including a cartridge case Ill and some usual propellant not shown. The fins 12 function as guides cooperating with inner wall surface of gun during movement toward the gun muzzle. Each of the four fins projects from ring 13 of fin material such as aluminum or alloys usually used for fins. In back of the fins is a sabot 14 of metal or plastic, for the purpose of enabling propellant pressure to raise the velocity of the projectile. After leaving the muzzle of the gun the four segments of the sabot 14 fall off from the projectile at as near simultaneoulsy as is possible in response to air pressure against a forward side of the sabot. Where some spin is to be imparted by rifling the radial outer edges of the fins together with the radial outer surface of the sabot cooperate with rifling for that purpose. In such event dowel pins '15 extend into the fins 12 and sabot 14.

At a rear end of projectile 10 is a soft metal bump ring 16 which is deformed and takes up considerable energy of the fins in moving rearward after the sabot segments have fallen olf. In place of or in addition to the shock absorbing ring 16, a ring 17 of either steel or softer metal is provided with a surface sloping slightly outward and rearward to function as an effective absorber of any energy of impact after the rear edge of the fins have passed ring 16. To absorb the forward thrust of propellant pressure against the sabot segments and transmit it effectively to the projectile body the radially inner surface of the sabot and the outer surface of the projectile under the sabot are each provided with cooperating buttress grooves 18 i.e. transverse lands and grooves of a diameter on body 10 not to impede rearward movement of the fins when the sabot segments have fallen off. A ring 19 of rubber or other material 19 extends 360 around a rear and tapered side of the sabot segment to transmit pro- 3,125,957: latented Mar. 24, 1964 2 pellant pressure to the sabot and then through the grooves 18 to the projectile.

Among the advantages of this improvement may be mentioned the fact that the smaller probable error is due to the center of gravity of the fins and sabot being located close to and substantially coincident with the center of gravity of the projectile body to provide the best interior ballistic behavior with less balloting. The sabot saves the fins from having their surfaces eroded as has occurred when the sabot is placed in front of the fins. The exterior ballistic operation of the fins have been moved rearward by air pressure early in flight.

This invention has been tried out in a 40 millimeter penetrator in a millimeter gun of both smooth bore and gradually rifled type to give a rotation of about 15 to 20 revolutions per second. With the centers of gravity close together as mentioned the failure of all sabot segments to fall away simultaneously appears to have less effect upon accuracy than can be expected with these segments remote from the fins and remote from the center of gravity of the projectile body. A sabot assists in raising the muzzle velocity to about 5000 feet per second. The center of gravity of the fins and sabot as a unit is made substantially coincident with the center of gravity indicated by the end of the lead line from numeral 20.

I claim:

1. In a fin stabilized projectile of the type having a penetrator body portion at least about 5 calibers in length and a sabot by means of which the muzzle velocity of said projectile may be raised, the combination therewith of the improvement for reducing balloting and erosion and heating of fin surfaces by hot products of combustion when said sabot is located in front of said fins, said improvement including, fins for stabilizing said projectile in flight, a sabot located contiguous to a rear end of said fins, said sabot being constructed of plural segments adapted to fall from said projectile during flight and in response to air pressure, a first abutment to transmit a forward thrust to said projectile from said sabot during forward movement in the gun, and a second abutment against which the fins impinge on being slid rearward by air pressure during an early portion of the projectile flight after leaving said gun and after said sabot segments have fallen away, the center of gravity of said fins and sabot as a unit being substantially coincident with the center of gravity of the projectile within the gun.

2. A projectile according to claim 1 in which said second abutment has at least some taper whereby its diameter is increased rearwardly to cushion the rearward movement of said fins along said projectile after said sabot segments have fallen away.

3. A projectile according to claim 2 in which said first abutment includes buttress lands and grooves on both the sabot and projectile which cooperate during movement of the projectile within a gun in which the projectile is fired.

4. A projectile according to claim 2 in which said second abutment includes a ring of softer material than is in said projectile.

5. A projectile according to claim 1 in which said second abutment includes a bump ring which deforms when said fins impinge thereagainst.

References Cited in the file of this patent UNITED STATES PATENTS 1,257,126 Schneider Feb. 19, 1918 2,798,433 Allen July 9, 1957 3,005,408 Prosen et a1. Oct. 24, 1961 3,005,409 Dunlap et a1. Oct. 24, 1961 FOREIGN PATENTS 603,139 Great Britain June 9, 1948 

1. IN A FIN STABLIZED PROJECTILE OF THE TYPE HAVING A PENETRATOR BODY PORTION AT LEAST ABOUT 5 CALIBERS IN LENGTH AND A SABOT BY MEANS OF WHICH THE MUZZLE VELOCITY OF SAID PROJECTILE MAY BE RAISED, THE COMBINATION THEREWITH OF THE IMPROVEMENT FOR REDUCING BALLOTING AND EROSION AND HEATING OF FIN SURFACES BY HOT PRODUCTS OF COMBUSTION WHEN SAID SABOT IS LOCATED IN FRONT OF SAID FINS, SAID IMPROVEMENT INCLUDING, FINS FOR STABILIZING SAID PROJECTILE IN FLIGHT, A SABOT LOCATED CONTIGUOUS TO A REAR END OF SAID FINS, SAID SABOT BEING CONSTRUCTED OF PLURAL SEGMENTS ADAPTED TO FALL FROM SAID PROJECTILE DURING FLIGHT AND IN RESPONSE TO AIR PRESSURE, A FIRST ABUTMENT TO TRANSMIT A FORWARD THRUST TO SAID PROJECTILE FROM SAID SABOT DURING FORWARD MOVEMENT IN THE GUN, AND A SECOND ABUTMENT AGAINST WHICH THE FINS IMPINGE ON BEING SLID REARWARD BY AIR PRESSURE DURING AN EARLY PORTION OF THE PROJECTILE FLIGHT AFTER LEAVING SAID GUN AND AFTER SAID SABOT SEGMENTS HAVE FALLEN AWAY, THE CENTER OF GRAVITY OF SAID FINS AND SABOT AS A UNIT BEING SUBSTANTIALLY COINCIDENT WITH THE CENTER OF GRAVITY OF THE PROJECTILE WITHIN THE GUN. 